Body temperature daily rhythms in the striped mouse Rhabdomys pumilio: The effects of α and/β blockade

Body temperature (Tb) daily rhythms and the effects of α and β blockade were studied in the South African diurnal striped mouse Rhabdomys pumilio. Eleven mice (8 males and 3 females) with a body mass of 42.7 ± 7.8 g (mean ± SD) were tested. Mice were acclimated to a 13 h: 11 h light-dark photoperiod at an ambient temperature of 25°C. To assess the dally rhythm of pineal melatonin secretion, urinary 6-sulfatoxymelatonin (6-SMT) was determined. Mice displayed a robust T(b) daily rhythm with an acrophase in the dark period, which is unexpected for a diurnal species. The nocturnal increase in T(b) was accompanied by a significant rise in urinary 6-SMT. The β blocker propranolol (4.5 mg/kg), injected 1 h before lights-off, resulted in a higher T(b) value, whereas the α blocker prazosin (1 mg/kg) blocked the increase of Tb during the dark period. Prazosin also significantly attenuated the nocturnal increase of urinary 6-SMT. These results are in agreement with those obtained from the golden spiny mouse Acomys russatus and support the idea that small diurnal mammals retain the Tb rhythm of a nocturnal rodent. They also suggest that pineal melatonin secretion in these rodents is regulated by α rather than by β receptors. Science Inc.